1. Field of the Invention
This invention relates to a method of manufacturing a molded wooden product by the compression molding under heat of a mass of wooden fibers containing a binder.
2. Description of the Prior Art
A molded wooden product of the type to which this invention pertains has a smaller weight than plywood and is superior in resistance to heat, water and moisture. Moreover, it is strong for its thickness. It is typically known as hardboard and is used for a wide range of applications including the decoration of the interior of houses, furniture or automobiles and the manufacture of television or stereo cabinets.
This kind of product has hitherto been manufactured by a method which will hereinafter be described. Wood chips are treated with steam having a temperature of 160.degree. C. to 180.degree. C. in a steaming tank in a splitting machine and are thereby loosened. The loosened chips are split into fibers by a splitting disk. The fibers are dried with hot air. Long fibers, such as of hemp or polypropylene, are added to the wooden fibers to improve their drawability. A binder composed of a phenol resin is added to bond the fibers. A water-repelling agent, such as rosin or paraffin, is also added to the fibers. The fibers and the additives are carefully mixed. The material which has been prepared as hereinabove described is formed into a stack having an appropriate thickness. The stack is lightly compressed under heat by a roll press to form a mat having a thickness of, for example, 10 to 40 mm, which is easy to carry. The mat is cut and placed in a mold in which it is compression molded at a temperature of 180.degree. C. to 220.degree. C. into an appropriately shaped product.
The method essentially includes the step of forming the mat and the step of cutting it into a particular shape. It is complicated and inefficient. Moreover, the mat is cut to a size which is larger than that of the final product and the excess of the material is cut away from the product. This is a waste of the material and the corresponding reduction of yield leads to a rise in the cost of production. The manufacture of a molded product having a deeply drawn portion from a single mat requires the use of a mat containing a large proportion (about 17%) of costly hemp fibers. Insofar as hemp fibers are used, it is necessary to add an extra amount of a synthetic resin. The product is, therefore, expensive.
Attempts have been made to form a mat containing a large amount or high percentage of wooden fibers preliminarily into the shape of a product before its final molding by treating it with steam to soften it and improve its deep drawability. The additional steps of manufacture, however, give rise to additional costs, for example, for equipment.
Also known is a wet molding method. A mixture of the split fibers prepared as hereinabove described, a synthetic resin, and cellulose paper are dispersed in water. The dispersion is subjected to filtration under pressure and compression, as when paper is made. The compressed product is compression molded under heat. This method is, however, necessarily expensive as it requires the use of special equipment for the pressurized filtration and compression of the material.